1. Technical Field
The invention relates to a safety valve capable of operating under high pressure and in the presence of a high flow rate. It applies particularly, but not exclusively, to valves which are placed notably at the head of hydrocarbon wells in order to close them for safety reasons.
2. Background Information
The use of spherical plug or ball valves as safety valves at well heads is well known. In their general structure, these valves include a valve body of generally cylindrical shape, a spherical plug or ball element mounted in this body for pivotal movement about an axis perpendicular to its bore, control means comprising a sliding sleeve capable of moving the ball between an open position and a closed position, and two seats with openings capable of defining a passage in the valve body with the bore of the ball when the latter is in the open position.
However, prior art valves exhibit various drawbacks. First of all, they make use in most cases of two stirrups around the ball element, one of which is designed to support it swivelably, and the other to actuate it between the open and closed positions. This arrangement leads to a large valve outer diameter.
Furthermore, with a two-stirrup mechanism of the type described above, the lever arm available for actuating the spherical plug is quite small.
The extent of this drawback will be better appreciated if it is noted that a safety valve for a well should be capable of operating under a pressure of 700 bars or more with a high flow rate corresponding to an internal passage of 7.62 centimeters (3 inches). With a small lever arm for the actuation of such a valve, it is necessary to provide a significant hydraulic pressure to actuate it.
Another problem encountered for safety valves is that during their actuation, they must be capable of cutting off different types of cables and tubes introduced through the ball element.